This project focuses on a recently discovered crosstalk between two protein families: high-voltage-activated Ca2+ (CaV) channels and the Rem/Rad/Gem/Kir (RGK) family of Ras-like GTPases. Ca2+ influx through CaV channels (ICa) regulates many essential processes including muscle contraction, synaptic communication, and gene expression. Dysregulation of ICa is linked to diverse neurological and cardiovascular disorders including autism and cardiac arrhythmias. Conversely, blockade of ICa is an important therapy for serious diseases such as angina, stroke, and hypertension. RGK GTPases were recently revealed to potently inhibit CaV channels by interacting with auxiliary CaVbeta subunits. Because RGK proteins are widely prevalent, and their expression differentially regulated in disease, their crosstalk with CaV channels is well-placed to regulate many Ca2+-dependent biological and pathophysiological events. Moreover, RGK GTPases represent a new archetype of ICa inhibitors that could be potentially exploited to generate novel genetically-encoded CaV-channel blockers with therapeutic and practical applications. We seek to address critical unknowns related to the action of RGK GTPases on CaV channels that limit insights into the (patho)physiological impact of this crosstalk, and its latent beneficial exploitation. Our long-term objective is to gain an in-depth understanding of mechanisms underlying the RGK GTPase/CaV-channel crosstalk and apply this knowledge to: (1) an appreciation of how this interaction contributes to (patho)physiology, and (2) create a new generation of useful genetically-encoded CaV- channel inhibitors. We propose 3 Aims: (1) Clarify the impact of RGK proteins on the gating and trafficking of CaV channels and elucidate the underlying mechanisms. (2) Characterize the functional impact of Ca2+- CaM on the RGK GTPase/CaV channel crosstalk. (3) Determine the expression profile of RGK GTPases in heart and define the functional impact of their crosstalk with L-type CaV channels. [unreadable] [unreadable]